Rotel RB 993 humming - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th January 2006, 01:57 PM   #1
diyAudio Member
 
Join Date: Apr 2003
Location: Paderborn, NRW
Send a message via ICQ to MichaelB
Question Rotel RB 993 humming

Hi,

I've recently purchased a used Rotel RB-993 3 channel amp on eBay
to accompany my RB-1080 for surround speakers.

Performs well but there is always a gentle humming noise (yes,
humming, no hiss...) coming from all three speakers. Not very
loud but clearly audible from all surround speakers in silent dvd
scenes.

I've checked cabling, transformer, everything, only speakers attached,
no change. Humming starts immediatly when the output relays turn on.
Power-supply seems to be ok, 74V DC with roughly 35mV AC on top
with no load.

Since the amp is a class-2 device (no earth at all) bad earth can't be
the reason. The transformer itself is dead silent, too.

Any ideas what could be the cause for the humming?
Maybe somebody experienced such effects with this amp before?

A pointer to the service manual might be helpfull, too.
  Reply With Quote
Old 8th January 2006, 02:05 PM   #2
diyAudio Moderator
 
pinkmouse's Avatar
 
Join Date: Apr 2002
Location: Chatham, England
Sounds like noise/ripple coming through from the PSU. You may have a dried up cap or faulty bridge diode. It may be a faulty component on the amp PCB, but as it is affecting all channels, that is less likely.
__________________
Rick: Oh Cliff / Sometimes it must be difficult not to feel as if / You really are a cliff / when fascists keep trying to push you over it! / Are they the lemmings / Or are you, Cliff? / Or are you Cliff?
  Reply With Quote
Old 9th January 2006, 09:43 PM   #3
diyAudio Member
 
Join Date: Dec 2004
Location: York
Hi,

are you sure this is not grounded?

I own one of theese wonderful amps as well. I got a buzzing aswell whenever my PC was plugged in (whether on or off).

I cut the ground wire in the 993, no buzz.

I am considering fitting a MOV in the gap but that should return it to being safe.

Check again that your unit has no ground, I am pretty sure mine did. If not how the hell did breaking the ground do anything if it was not there to start with!
  Reply With Quote
Old 9th January 2006, 10:06 PM   #4
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi MichaelB,
Does it hum if the inputs are not plugged in? Do you have cable hooked up?

-Chris
  Reply With Quote
Old 9th January 2006, 10:12 PM   #5
Banned
 
Join Date: Mar 2005
Location: Australia
Anatech by the sound of it is not a ground loop, of course they are hooked up
whats your diagnosis

cheers
  Reply With Quote
Old 10th January 2006, 01:00 AM   #6
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi mastertech,
One never can tell until the basic tests are done. If cable is involved, the cable ground can be the largest, most evil ground loop ever designed.

So it's time to gather information.

-Chris
  Reply With Quote
Old 10th January 2006, 03:20 AM   #7
Banned
 
Join Date: Mar 2005
Location: Australia
what if isnt that (grd loop) and there is still some light hum as the
fellow has said on very low audio levels, whats your diagnosis
  Reply With Quote
Old 10th January 2006, 06:40 AM   #8
diyAudio Member
 
Join Date: Apr 2003
Location: Paderborn, NRW
Send a message via ICQ to MichaelB
Hi,

the mains plug has no earth contacts, so it can't be an earth loop.

No input cables attached, only speakers, there is humming from the
speakers. Having my pre connected or not makes no difference.

The source for the hum has to be somewhere in the amps circuitry,
most likely the PSU, as pinkmouse suggested, since all three channels
produce humming noise.

I will check the PSU more closely as soon a I have some spare time
again.

Does anybody by chance have the service manual available?
  Reply With Quote
Old 10th January 2006, 06:43 AM   #9
diyAudio Member
 
Tube_Dude's Avatar
 
Join Date: Mar 2002
Location: Aveiro-Portugal
Is the signal ground connected to the case?
__________________
Jorge
  Reply With Quote
Old 10th January 2006, 07:14 AM   #10
diyAudio Member
 
Join Date: Dec 2004
Location: York
just one extra. After a quick chat fitting an MOV in line with earth does not make it safe, well safer than not at all.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Service Manual/ schematic for Rotel ROTEL RHCD-10 Michi CD player Staykov Digital Source 5 16th May 2012 12:24 AM
Rotel RC-850 Pre Amp + Rotel RB-870BX bleachershane Analog Line Level 4 9th February 2009 11:20 AM
Humming Jorgitox Solid State 19 29th November 2007 02:42 PM
Rotel RX950 with humming noise jorgens Solid State 1 28th March 2007 08:34 PM
humming amp Pumuckel Pass Labs 10 26th February 2004 12:40 AM


New To Site? Need Help?

All times are GMT. The time now is 10:16 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2